Anything wrong with adding require '/path/to/master.php'; to each of the settings.php files?
– Clive♦Nov 4 '13 at 18:46

@Clive Ask the developers who take over this project and don't know about the master.php file. (but that's probably what I'll end up doing if there's no native Drupal solution)
– Alan StormNov 4 '13 at 18:50

I'd imagine that info would be on the handover docs but I get what you're saying. Hard to think of a native Drupal solution, Because of the way settings.php is included I think you're out of luck (short of server wizardry, but that has the same problem you've already mentioned)
– Clive♦Nov 4 '13 at 18:55

2 Answers
2

so for what it's worth using the default/settings.php as the master and then having each of the sites do a PHP include (as @Alan mentions) does work well! (I know this is an old question but I am working through multisite issues with Drupal 8 (8.6.13) and have come across this very thing...)

a couple of caveats:

1) I am managing the multisite installation and config manually so am creating my ownsettings.php files, not using drush site-install which will auto-generate the settings.php

2) you must do the include at the top of the site's settings.php and ensure that you are overriding only what you need to. (...or the inverse, that you are okay using the config in the default settings file)